1. Field of the Invention
The present invention relates to a cosmetic material offering excellent sensory characteristics, improved dissolution stability of poorly soluble components such as UV absorbents, excellent compatibility with silicone oil, excellent dispersion stability of pigments and colorants, and excellent safety.
The present invention also relates to a cosmetic material that blends, as a dissolution stabilizer, an octyl hydroxy stearate oligomer selected from a dimer to heptamer of octyl hydroxy stearate (hereinafter simply referred to as “octyl hydroxy stearate oligomer”).
More specifically, the present invention relates to a cosmetic material that does not cause separation and precipitation over time of poorly soluble components used in cosmetic materials and known as crystalline long-wavelength UV absorbents that crystallize and precipitate easily during preservation, such as diethyl amino hydroxy benzoyl hexyl benzoate and 4-tert-buthyl-4′-methoxy dibenzoyl methane, and offers excellent UV shielding effect, sensory characteristics, dispersion stability of pigments and colorants, and color development property.
2. Description of Related Art
Traditionally, octyl hydroxy stearate (also known as 2-ethyl hexyl hydroxy stearate) has been a type of oil solution used in cosmetic materials, as described in Patent Literatures 1 to 3. Hydroxy stearate and its oligomer, which are compounds of the same type, are also used in cosmetic materials as described in Patent Literatures 4 to 6.
Hydroxy stearate, which is a source compound of the aforementioned octyl hydroxy stearate, is itself a compound derived from plant-based castor oil. Due in part to the booming use of natural plant-based ingredients in recent years, octyl hydroxy stearate is drawing the attention as a material for making cosmetic products.
As for examples of use of octyl hydroxy stearate, examples of a derivative of hydroxy stearate or its oligomer include zinc 12-hydroxy stearate as described in Patent Literature 7, dipentaerythrityl 12-hydroxy stearate ester, phytosteryl hydroxy stearate and dipentaerythrityl hexa (hydroxy stearate, stearate, rosinate) as described in Patent Literature 8, amide 12-hydroxy stearate as described in Patent Literature 9, polyglycerin ester being a self-condensation product of hydroxy stearate and polyethylene glycol ester also being a self-condensation product of hydroxy stearate as described in Patent Literature 10, and cholesteryl 12-hydroxy stearate as described in Patent Literature 11, all of which are reported as components of cosmetic materials and subject to various examinations.
As described above, hydroxy stearate and its oligomer as well as any derivative thereof, such as octyl hydroxy stearate, are known to be used for cosmetic material applications. However, no examples are found where an oligomer of octyl hydroxy stearate is used for any cosmetic material application.
Being a component used for cosmetic material applications, diethyl amino hydroxy benzoyl hexyl benzoate is known as a UV absorbent because it has a function to absorb long-wavelength UV light. However, its use in cosmetic materials presents problems because diethyl amino hydroxy benzoyl hexyl benzoate is poorly soluble and its crystalline content precipitates in the solution over time.
For example, diethyl amino hydroxy benzoyl hexyl benzoate is mentioned as UV absorbent No. 37 (paragraph 0085) in a cosmetic material disclosed in Patent Literature 12, and also in paragraph 0037 in a UV shielding composition disclosed in Patent Literature 13. In Patent Literature 14, this diethyl amino hydroxy benzoyl hexyl benzoate is made into fine grain powder and blended into a cosmetic material, while in Patent Literature 15 it is blended with 2,4,6-trianilino-p-(carbo-2′-ethyl hexyl-1′-oxy)-1,3,5-triazine and the resulting powder mixture is blended, in a fine powder form, into a cosmetic material.
Since these UV absorbents present problems in terms of their solubility (Patent Literature 15, paragraph 0012), technologies have been reported to convert UV absorbents into nano-powder and blend this nano-powder into a cosmetic materials for the purpose of improving the solubility of these UV absorbents (Patent Literature 16). However, a fundamental problem has been to blend not just diethyl amino hydroxy benzoyl hexyl benzoate, but all UV absorbents, as well, into cosmetic materials in a stable manner without causing dispersion problems.
Diethyl amino hydroxy benzoyl hexyl benzoate has poor solubility in various oil solutions and solvents, and octyl para-methoxy cinnamate (same compound as 2-ethyl hexyl para-methoxy cinnamate) is known as a solvent that can dissolve diethyl amino hydroxy benzoyl hexyl benzoate to a certain degree.
For example, Non-patent Literature 1 shows that diethyl amino hydroxy benzoyl hexyl benzoate dissolves by 42% when 2-ethyl hexyl para-methoxy cinnamate is used as a solvent. However, the solution actually obtained this way presents a problem of diethyl amino hydroxy benzoyl hexyl benzoate crystallizing and precipitating in autumn and winter seasons when temperatures drop.
Non-patent Literature 1 also shows that diethyl amino hydroxy benzoyl hexyl benzoate dissolves only by 0.4% in cyclomethicone, which is a type of volatile silicone.
In Japan and Southeast Asia where the environment is hot and humid, silicone compounds, especially cyclomethicone, are used in large quantities in most sunscreen products for recreational use for the purpose of ensuring resistance to water and sweat. If diethyl amino hydroxy benzoyl hexyl benzoate is blended in sunscreen products used under these conditions, it will precipitate easily. It seems Patent Literatures 14 and 15 mentioned earlier attempted to blend diethyl amino hydroxy benzoyl hexyl benzoate into cosmetic materials without dissolving it, after taking into consideration the fact that diethyl amino hydroxy benzoyl hexyl benzoate is poorly soluble.
As explained above, diethyl amino hydroxy benzoyl hexyl benzoate has poor compatibility with silicone-based cosmetics, and how to improve the solubility of this diethyl amino hydroxy benzoyl hexyl benzoate has been a big problem in the field of cosmetics.
On the other hand, Patent Literatures 17 and 18 introduce a number of examples pertaining to a cosmetic materials in which diethyl amino hydroxy benzoyl hexyl benzoate is blended (brand name: Uvinul A Plus (registered trademark)). However, no methods of manufacturing these examples are shown, and therefore how diethyl amino hydroxy benzoyl hexyl benzoate is dissolved is unknown. In addition, the aforementioned patent literatures use Uvinul A Plus (registered trademark) in powder form, instead of using Uvinul A Plus B (registered trademark) which is another commercially available product constituted by diethyl amino hydroxy benzoyl hexyl benzoate dissolved in octyl para-methoxy cinnamate. Accordingly, whether diethyl amino hydroxy benzoyl hexyl benzoate is actually dissolved is not certain and its stability is not evaluated, either.
As described above, diethyl amino hydroxy benzoyl hexyl benzoate having a function to absorb long-wavelength UV light is in many cases blended as a powder dispersant, as described in Patent Literatures 14 and 15, due to its poor solubility. On the other hand, no means are reported to make diethyl amino hydroxy benzoyl hexyl benzoate more easily soluble.
UV absorbents can be blended in different ways, such as blending into a cosmetic materials as powder or dissolving first and then blending as solution, where in many cases the UV shielding effect per unit blended quantity changes according to the blending method.
In general, the UV shielding effect of a UV absorbent drops when the UV absorbent is blended as powder, compared to when it is dissolved and then blended. This is because when the UV absorbent is blended as powder, gaps are created between powder grains and UV light passes through these gaps to reach the skin, thereby lowering the UV shielding effect in areas where UV light reaches the skin. If the blended quantity of the UV absorbent is the same, a stronger UV shielding effect can be achieved by blending the UV absorbent as solution, and for this reason there is a greater need to use UV absorbents as solution in cosmetic products.
As explained above, cosmetic materials can have a greater UV shielding effect when they blend a UV absorbent in a stable manner, or specifically when they blend a UV absorbent as solution. In addition, the market is also awaiting development of cosmetic products that are resistant to water and sweat, and the needs for UV absorbents suitable in these applications are growing also in the international market.
Just like the problem of poor solubility of the UV absorbent diethyl amino hydroxy benzoyl hexyl benzoate mentioned above, 4-tert-butyl-4′-methoxy dibenzoyl methane which also has a function to shield UV light presents a similar problem.
For example, Patent Literature 19 describes improving the solubility and stability of 4-tert-butyl-4′-methoxy dibenzoyl methane by combining an effective quantity of a silane or organosiloxane compound having a benzylidene camphor functional group and a dibenzoyl methane derivative and then mixing the combined ingredients into a support that can be used in cosmetic products to produce a composition, thereby improving the optical stability and solubility of dibenzoyl methane derivative. On the other hand, Patent Literature 20 describes an optically stable, light-shielding composition for cosmetic or medical use that contains a dibenzoyl methane UV-A shielding agent and p-methoxy cinnamate UV-B shielding agent, where one of the aforementioned shielding agents is incorporated into a polymer matrix.
Furthermore, Patent Literature 21 describes a cosmetic composition for local use for the purpose of protecting skin and/or hair from light, wherein such cosmetic composition contains, in a carrier that can be used in cosmetic products, a target shielding component to be dissolved which is selected from 4-methyl benzylidene camphor (compound A), 4-(tert-butyl)-4′-methoxy dibenzoyl methane (compound B) and a mixture thereof, where such composition is manufactured by dissolving the aforementioned target shielding component to be dissolved through use of a soluble shielding component selected from homomethyl salicylate (compound C), octyl salicylate (compound D) and a mixture thereof, and where enough quantity of this soluble shielding component is used to dissolve all of the aforementioned target shielding component to be dissolved. However, these technologies fail to blend 4-tert-butyl-4′-methoxy dibenzoyl methane in a stable manner in cosmetic formulations with ease, and many examinations are underway to achieve stable blending.
However, cosmetic products currently available on the market only contain a small amount of 4-tert-butyl-4′-methoxy dibenzoyl methane, and the problem has to do with the difficulty in blending a sufficient quantity of 4-tert-butyl-4′-methoxy dibenzoyl methane to achieve a level of stability that warrants industrial applications.
There are many liquid organic UV absorbents that absorb medium-wavelength UV light, few of which present major blending problems that would result in precipitation or crystallization, and therefore no serious problems have been reported so far. As the negative effects of long-wavelength UV light became a point of discussion in recent years, long-wavelength UV absorbents have been drawing the attention. However, not many known components are available that can be used as long-wavelength UV absorbents, and many of these known components are poorly soluble and crystalline in nature. Accordingly, there is an urgent need to study dissolution stabilizers capable of achieving stable dissolution and use, in cosmetic materials, of diethyl amino hydroxy benzoyl hexyl benzoate, 4-tert-butyl-4′-methoxy dibenzoyl methane and other crystalline components that are known as long-wavelength UV absorbents, as described above.    [Patent Literature 1] Japanese Patent Laid-open No. 2001-58915    [Patent Literature 2] Japanese National Publication of Translation No. 2004-510718    [Patent Literature 3] Japanese Patent Laid-open No. 2006-273820    [Patent Literature 4] Japanese Patent Laid-open No. 2008-106050    [Patent Literature 5] Japanese Patent Laid-open No. 2008-94791    [Patent Literature 6] Japanese Patent Laid-open No. 2007-277400    [Patent Literature 7] Japanese Patent Laid-open No. 2007-291025    [Patent Literature 8] Japanese Patent Laid-open No. 2007-262033    [Patent Literature 9] Japanese Patent Laid-open No. 2007-63164    [Patent Literature 10] Japanese Patent Laid-open No. 2006-281182    [Patent Literature 11] Japanese Patent Laid-open No. 2001-270815    [Patent Literature 12] U.S. Patent No. US2005/0255057A1    [Patent Literature 13] U.S. Patent No. US2007/0160549A1    [Patent Literature 14] U.S. Patent No. US2007/0031352A1    [Patent Literature 15] U.S. Patent No. US2007/0028401A1    [Patent Literature 16] U.S. Patent No. US2007/0025931A1    [Patent Literature 17] Published Japanese translation of PCT International Patent Application No. 2005-513093    [Patent Literature 18] Published Japanese translation of PCT International Patent Application No. 2005-513094    [Patent Literature 19] Japanese Patent Laid-open No. 2004-107349    [Patent Literature 20] Japanese Patent Laid-open No. 2000-351721    [Patent Literature 21] Japanese Patent Laid-open No. Hei 11-71255    [Non-patent Literature 1] (Uvinul A Plus) New Stable & Long-lasting UV-A UV Absorbent, www.matsumoto-trd.co.jp/product/pdf/01/15/A.pdf (Searched on Jun. 30, 2008)